We evaluated the reliability of static and dynamic lumbar muscle endurance measurements on a BackUP lumbar extension dynamometer. Sixteen healthy participants (8 male; 8 female) volunteered for this investigation. Fifty percent of each participant's body weight was calculated to determine the weight load utilized for the static (holding time) and dynamic (repetitions) lumbar extension endurance tests. Four separate tests (2 static, 2 dynamic) were conducted with at least a 24-hour rest period between tests. Test-retest intraclass correlations were shown to be high (static lumbar endurance, ICC = 0.92 (p < 0.0005); dynamic lumbar endurance, ICC = 0.93 (p < 0.0005) for both of the performed tests. Our results demonstrated that static and dynamic lumbar endurance can be assessed reliably on a BackUP lumbar extension dynamometer. Key PointsReliability studies that test lumbar endurance on machines that effectively stabilize the pelvis and isolate the lumbar extensors are limited.This is the first study to report reliability measures of static and dynamic lumbar endurance on a BackUP lumbar extension dynamometer.Static and dynamic lumbar endurance on a BackUP lumbar extension dynamometer, which uses a variety of pelvic stabilization mechanisms, can be reliably assessed in apparently healthy individuals.Future research is necessary to examine the reliability of lumbar extension endurance on the BackUP dynamometer in patient populations and validity in various settings.